Ocean Drilling Program Legs 170 and 205 focused on the hydrogeology of the Costa Rica subduction zone (Kimura, Silver, Blum, et al., 1997; Morris, Villinger, Klaus, et al., 2003). Intrinsic permeability is an important property of the porous medium that controls fluid flow in sediments. In this study, we used core samples from one site from Leg 170 and two sites from Leg 205 to measure vertical permeabilities (Fig. F1). To further characterize the sediments, grain size, inorganic carbon, and total carbon analyses were conducted.